He's in China, so there's probably little you can do to stop it, other than researching everything upstream from him and fighting with them. Since he's sending from what is probably a legitimate address you could filter the entire domain. He does own the domain, so it's doubtful he can do business without including it somewhere in his headers or the body of his message. Of course he could use a forwarder to hide it, but that would just complicate things for him and make him a bit more vulnerable.
It could be that he's not really trying to sell you a flashlight, but is looking for live active addresses for selling lists. Filtering is about the best thing to do. There's ways of turning his computer life into a living nightmare but it takes time and a lot of effort.